1. Field of the Invention
The present invention pertains to a system for processing radar video signals and more particularly to a digital processing system for ascertaining the range and angle centroids of detected targets in track while scan radar systems.
2. Description of the Prior Art
In a track while scan radar system target location and tracks are automatically computed from video data derived from the radar signal returns. This automatic determination of target range and azimuth present major computational problems. During each scan, radar target returns in any given range cell are compared to a preselected threshold and a hit is declared when the return exceeds this threshold. Data in a given range cell is correlated over a number of transmissions and a target is generally declared when a hit is recorded from M of N transmissions. To minimize the probability of recording a hit on a noise spike or other spurious responses (fruit), defruiting circuits are generally inserted between the threshold comparison and detecting networks. This technique provides adequate detection criteria but ambiguous information may be established when large targets are encountered which cause significant target energy to appear in more than one angular cell. Defruiting circuits of the prior art allow a hit to be recorded either when the M.sup.th return and any one of the M-1 previous returns indicate a target or the first of M returns and any one of the succeeding M-1 returns indicate a target. These systems are asymmetrical, bias the target angle data towards the first or M.sup.th return and lose one pulse in each pulse train.
Additionally, the relatively wide angular coverage of a typical radar antenna presents a serious problem in the determination of the true angular location of the target, and targets that extend over several range cells present an ambiguity regarding the location of the target's range centroid. The range centroid of an extruded target is generally determined by establishing the range over which the target extends and taking the center thereof. To determine the location of a target within the antenna beam, techniques known as beam splitting have been employed. The most successful beam splitting technique of the prior art incorporate weighting factors applied to the video derived from each radar return. Generally, the weights have odd symmetry about the beam center and the angular location of the target is determined from the central beam position in the angular range for which the sum of the weighted returns is zero as the antenna beam sweeps past the target. The accuracy of these systems is a function of the antenna beam symmetry, the target signal to noise ratio and the target fluctuations, thus requiring antennas with beam symmetry and with high signal to noise ratios.